Nervous system is the basis of any kind of interaction of living beings in the surrounding world, as well as a system for maintaining homeostasis in multicellular organisms. The higher the organization of a living organism, the more complex the nervous system is. The basic unit of the nervous system is neuron- a cell that has short processes of dendrites and a long process of axon.
The human nervous system can be conditionally divided into CENTRAL and PERIPHERAL, as well as separately identified autonomic nervous system, which has its representation both in the departments of the central and in the departments of the peripheral nervous systems. The central nervous system consists of the brain and spinal cord, and the peripheral nervous system consists of the nerve roots of the spinal cord, cranial, spinal and peripheral nerves, as well as nerve plexuses.
BRAIN comprises:
two hemispheres
cerebrum brainstem,
cerebellum.
Hemispheres of the brain divided into frontal lobes, parietal, temporal and occipital lobes. The hemispheres of the brain are connected through the corpus callosum.
- The frontal lobes are responsible for the intellectual and emotional sphere, thinking and complex behavior, conscious movements, motor speech and writing skills.
- The temporal lobes are responsible for hearing, sound perception, vestibular information, partial analysis of visual information (for example, face recognition), sensory part of speech, participation in memory formation, influence on the emotional background, for influence on the autonomic nervous system through communication with the limbic system.
- The parietal lobes are responsible for various types of sensitivity (tactile, pain temperature, deep and complex spatial types of sensitivity), spatial orientation and spatial skills, reading, counting.
- Occipital lobes - perception and analysis of visual information.
brain stem represented by the diencephalon (thalamus, epithalamus, hypothalamus and pituitary), midbrain, pons and medulla oblongata. Functions of the brain stem responsible for unconditioned reflexes, influence on the extrapyramidal system, gustatory, visual, auditory and vestibular reflexes, suprasegmental level of the autonomic system, control of the endocrine system, regulation of homeostasis, hunger and satiety, thirst, regulation of the sleep-wake cycle, regulation of respiration and the cardiovascular system , thermoregulation.
Cerebellum consists of two hemispheres and a worm that connects the hemispheres of the cerebellum. Both the cerebral hemispheres and the cerebellar hemispheres are striated with furrows and convolutions. The cerebellar hemispheres also contain nuclei with gray matter. The cerebellar hemispheres are responsible for coordination of movements and vestibular function, and the cerebellar vermis is responsible for maintaining balance and postures, muscle tone. The cerebellum also influences the autonomic nervous system. There are four ventricles in the brain, in the system of which CSF circulates and which are connected with the subarachnoid space of the cranial cavity and spinal canal.
Spinal cord consists of the cervical, thoracic, lumbar and sacral regions, has two thickenings: the cervical and lumbar, and the central spinal canal (in which the cerebrospinal fluid circulates and which in the upper sections connects to the fourth ventricle of the brain).
Histologically, brain tissues can be divided into Gray matter, which contains neurons, dendrites (short processes of neurons) and glial cells, and white matter, in which axons lie, long processes of neurons covered with myelin. In the brain, gray matter is located mainly in the cerebral cortex, in the basal nuclei of the hemispheres and the nuclei of the brain stem (midbrain, bridge and medulla oblongata), and in the spinal cord, gray matter is located in depth (in its central sections), and the outer parts of the spinal cord are represented by white matter.
Peripheral nerves can be divided into motor and sensory, forming reflex arcs that are controlled by parts of the central nervous system.
autonomic nervous system has a division into suprasegmental And segmental.
- The suprasegmental nervous system is located in the limbic-reticular complex (structures of the brain stem, hypothalamus and limbic system).
- The segmental part of the nervous system is divided into the sympathetic, parasympathetic and metasympathetic nervous systems. The sympathetic and parasympathetic nervous systems are also divided into central and peripheral. The central divisions of the parasympathetic nervous system are located in the midbrain and medulla oblongata, and the central divisions of the sympathetic nervous system are located in the spinal cord. The metasympathetic nervous system is organized by nerve plexuses and ganglia in the walls of the internal organs of the chest (heart) and abdominal cavity (intestines, bladder, etc.).
Nerve endings are located throughout the human body. They have an important function and are integral part the entire system. The structure of the human nervous system is a complex branched structure that runs through the entire body.
The physiology of the nervous system is a complex composite structure.
The neuron is considered the basic structural and functional unit of the nervous system. Its processes form fibers that are excited when exposed and transmit an impulse. The impulses reach the centers where they are analyzed. After analyzing the received signal, the brain transmits the necessary reaction to the stimulus to the appropriate organs or parts of the body. The human nervous system is briefly described by the following functions:
- providing reflexes;
- regulation of internal organs;
- ensuring the interaction of the organism with the external environment, by adapting the body to changing external conditions and stimuli;
- interaction of all organs.
The value of the nervous system is to ensure the vital activity of all parts of the body, as well as the interaction of a person with the outside world. The structure and functions of the nervous system are studied by neurology.
Structure of the CNS
Anatomy of the central nervous system (CNS) is a collection of neuronal cells and neuronal processes of the spinal cord and brain. A neuron is a unit of the nervous system.
The function of the central nervous system is to provide reflex activity and process impulses coming from the PNS.
The anatomy of the central nervous system, the main node of which is the brain, is a complex structure of branched fibers.
The higher nerve centers are concentrated in the cerebral hemispheres. This is the consciousness of a person, his personality, his intellectual abilities and speech. The main function of the cerebellum is to ensure coordination of movements. The brain stem is inextricably linked to the hemispheres and the cerebellum. This section contains the main nodes of the motor and sensory pathways, which ensures such vital body functions as the regulation of blood circulation and breathing. The spinal cord is the distribution structure of the CNS, it provides branching of the fibers that form the PNS.
The spinal ganglion (ganglion) is the site of concentration of sensitive cells. With the help of the spinal ganglion, the activity of the autonomic division of the peripheral nervous system is carried out. Ganglia or nerve nodes in the human nervous system are classified as PNS, they perform the function of analyzers. The ganglia do not belong to the human central nervous system.
Structural features of the PNS
Thanks to the PNS, the activity of the entire human body is regulated. The PNS is made up of cranial and spinal neurons and fibers that form ganglia.
The structure and functions of the human peripheral nervous system are very complex, so any slightest damage, for example, damage to the vessels in the legs, can cause serious disruption of its work. Thanks to the PNS, control is exercised over all parts of the body and the vital activity of all organs is ensured. The importance of this nervous system for the body cannot be overestimated.
The PNS is divided into two divisions - the somatic and autonomic systems of the PNS.
The somatic nervous system performs a double job - collecting information from the sense organs, and further transferring this data to the central nervous system, as well as ensuring the motor activity of the body, by transmitting impulses from the central nervous system to the muscles. Thus, it is the somatic nervous system that is the instrument of human interaction with the outside world, since it processes the signals received from the organs of vision, hearing and taste buds.
The autonomic nervous system ensures the performance of the functions of all organs. It controls the heartbeat, blood supply, and respiratory activity. It contains only motor nerves that regulate muscle contraction.
To ensure the heartbeat and blood supply, the efforts of the person himself are not required - it is the vegetative part of the PNS that controls this. The principles of the structure and function of the PNS are studied in neurology.
Departments of the PNS
The PNS also consists of an afferent nervous system and an efferent division.
The afferent section is a collection of sensory fibers that process information from receptors and transmit it to the brain. The work of this department begins when the receptor is irritated due to any impact.
The efferent system differs in that it processes impulses transmitted from the brain to effectors, that is, muscles and glands.
One of the important parts of the autonomic division of the PNS is the enteric nervous system. The enteric nervous system is formed from fibers located in the gastrointestinal tract and urinary tract. The enteric nervous system controls the motility of the small and large intestines. This department also regulates the secretion secreted in the gastrointestinal tract and provides local blood supply.
The value of the nervous system is to ensure the work of internal organs, intellectual function, motor skills, sensitivity and reflex activity. The central nervous system of a child develops not only in the prenatal period, but also during the first year of life. The ontogenesis of the nervous system begins from the first week after conception.
The basis for the development of the brain is formed already in the third week after conception. The main functional nodes are indicated by the third month of pregnancy. By this time, the hemispheres, trunk and spinal cord have already been formed. By the sixth month, the higher parts of the brain are already better developed than the spinal region.
By the time the baby is born, the brain is the most developed. The size of the brain in a newborn is approximately one eighth of the weight of the child and fluctuates within 400 g.
The activity of the central nervous system and PNS is greatly reduced in the first few days after birth. This may be in the abundance of new irritating factors for the baby. This is how the plasticity of the nervous system is manifested, that is, the ability of this structure to rebuild. As a rule, the increase in excitability occurs gradually, starting from the first seven days of life. The plasticity of the nervous system deteriorates with age.
CNS types
In the centers located in the cerebral cortex, two processes simultaneously interact - inhibition and excitation. The rate at which these states change determines the types of the nervous system. While one section of the CNS center is excited, the other is slowed down. This is the reason for the peculiarities of intellectual activity, such as attention, memory, concentration.
Types of the nervous system describe the differences between the speed of the processes of inhibition and excitation of the central nervous system in different people.
People may differ in character and temperament, depending on the characteristics of the processes in the central nervous system. Its features include the speed of switching neurons from the process of inhibition to the process of excitation, and vice versa.
Types of the nervous system are divided into four types.
- The weak type, or melancholic, is considered the most prone to the occurrence of neurological and psycho-emotional disorders. It is characterized by slow processes of excitation and inhibition. A strong and unbalanced type is a choleric. This type is distinguished by the predominance of excitatory processes over inhibition processes.
- Strong and mobile - this is the type of sanguine. All processes occurring in the cerebral cortex are strong and active. Strong, but inert, or phlegmatic type, characterized by a low rate of switching of nervous processes.
Types of the nervous system are interconnected with temperaments, but these concepts should be distinguished, because temperament characterizes a set of psycho-emotional qualities, and the type of the central nervous system describes physiological features processes in the CNS.
CNS protection
The anatomy of the nervous system is very complex. The CNS and PNS suffer from the effects of stress, overexertion, and malnutrition. Vitamins, amino acids and minerals are necessary for the normal functioning of the central nervous system. Amino acids are involved in brain function and are building material for neurons. Having figured out why and what vitamins and amino acids are needed for, it becomes clear how important it is to provide the body with the necessary amount of these substances. Glutamic acid, glycine and tyrosine are especially important for humans. The scheme of taking vitamin-mineral complexes for the prevention of diseases of the central nervous system and PNS is selected individually by the attending physician.
Damage to bundles of nerve fibers, congenital pathologies and anomalies in the development of the brain, as well as the action of infections and viruses - all this leads to disruption of the central nervous system and PNS and the development of various pathological conditions. Such pathologies can cause a number of very dangerous diseases - immobilization, paresis, muscle atrophy, encephalitis and much more.
Malignant neoplasms in the brain or spinal cord lead to a number of neurological disorders. If you suspect an oncological disease of the central nervous system, an analysis is prescribed - the histology of the affected departments, that is, an examination of the composition of the tissue. A neuron, as part of a cell, can also mutate. Such mutations can be detected by histology. Histological analysis is carried out according to the testimony of a doctor and consists in collecting the affected tissue and its further study. With benign formations, histology is also performed.
There are many nerve endings in the human body, damage to which can cause a number of problems. Damage often leads to a violation of the mobility of a part of the body. For example, an injury to the hand can lead to pain in the fingers and impaired movement. Osteochondrosis of the spine provoke the occurrence of pain in the foot due to the fact that an irritated or transmitted nerve sends pain impulses to receptors. If the foot hurts, people often look for the cause in a long walk or injury, but the pain syndrome can be triggered by damage to the spine.
If you suspect damage to the PNS, as well as any related problems, you should be examined by a specialist.
The nervous system controls the activity of all systems and organs and ensures the connection of the body with the external environment.
The structure of the nervous system
The structural unit of the nervous system is the neuron - a nerve cell with processes. In general, the structure of the nervous system is a collection of neurons that are constantly in contact with each other using special mechanisms - synapses. The following types of neurons differ in function and structure:
- Sensitive or receptor;
- Effector - motor neurons that send an impulse to the executive organs (effectors);
- Closing or plug-in (conductor).
Conventionally, the structure of the nervous system can be divided into two large sections - somatic (or animal) and vegetative (or autonomous). The somatic system is primarily responsible for the connection of the body with the external environment, providing movement, sensitivity and contraction of skeletal muscles. The vegetative system affects the growth processes (respiration, metabolism, excretion, etc.). Both systems have a very close relationship, only the autonomic nervous system is more independent and does not depend on the will of a person. That is why it is also called autonomous. The autonomous system is divided into sympathetic and parasympathetic.
The entire nervous system consists of the central and peripheral. The central part includes the spinal cord and brain, and the peripheral system represents the outgoing nerve fibers from the brain and spinal cord. If you look at the brain in section, you can see that it consists of white and gray matter.
Gray matter is an accumulation of nerve cells (with the initial sections of processes extending from their bodies). Separate groups of gray matter are also called nuclei.
White matter consists of nerve fibers covered with myelin sheath (processes of nerve cells from which gray matter is formed). In the spinal cord and brain, nerve fibers form pathways.
Peripheral nerves are divided into motor, sensory and mixed, depending on what fibers they consist of (motor or sensory). The bodies of neurons, whose processes are made up of sensory nerves, are located in ganglions outside the brain. The bodies of motor neurons are located in the motor nuclei of the brain and the anterior horns of the spinal cord.
Functions of the nervous system
The nervous system has different effects on the organs. The three main functions of the nervous system are:
- Starting, causing or stopping the function of an organ (secretion of the gland, muscle contraction, etc.);
- Vasomotor, which allows you to change the width of the lumen of the vessels, thereby regulating the flow of blood to the organ;
- Trophic, lowering or increasing metabolism, and, consequently, the consumption of oxygen and nutrients. This allows you to constantly reconcile functional state body and its need for oxygen and nutrients. When impulses are sent along the motor fibers to the working skeletal muscle, causing its contraction, then impulses are simultaneously received that increase metabolism and dilate blood vessels, which makes it possible to provide an energy opportunity to perform muscle work.
Diseases of the nervous system
Together with the endocrine glands, the nervous system plays a crucial role in the functioning of the body. It is responsible for the coordinated work of all systems and organs of the human body and unites the spinal cord, brain and peripheral system. Motor activity and sensitivity of the body is supported by nerve endings. And thanks to the autonomic system, the cardiovascular system and other organs are inverted.
Therefore, a violation of the functions of the nervous system affects the work of all systems and organs.
All diseases of the nervous system can be divided into infectious, hereditary, vascular, traumatic and chronically progressive.
Hereditary diseases are genomic and chromosomal. The most famous and common chromosomal disease is Down's disease. This disease is characterized by the following symptoms: a violation of the musculoskeletal system, the endocrine system, lack of mental abilities.
Traumatic lesions of the nervous system occur due to bruises and injuries, or when squeezing the brain or spinal cord. Such diseases are usually accompanied by vomiting, nausea, memory loss, disorders of consciousness, loss of sensitivity.
Vascular diseases mainly develop against the background of atherosclerosis or hypertension. This category includes chronic cerebrovascular insufficiency, cerebrovascular accident. Characterized by the following symptoms: bouts of vomiting and nausea, headache, impaired motor activity, decreased sensitivity.
Chronically progressive diseases, as a rule, develop as a result of metabolic disorders, exposure to infection, intoxication of the body, or due to anomalies in the structure of the nervous system. Such diseases include sclerosis, myasthenia, etc. These diseases usually progress gradually, reducing the efficiency of some systems and organs.
Causes of diseases of the nervous system:
The placental route of transmission of diseases of the nervous system during pregnancy (cytomegalovirus, rubella), as well as through the peripheral system (poliomyelitis, rabies, herpes, meningoencephalitis) is also possible.
In addition, the nervous system is negatively affected by endocrine, heart, kidney diseases, malnutrition, chemicals and drugs, heavy metals.
❖ The human nervous system is represented by:
■ the brain and spinal cord (together they form central nervous system
);
■ nerves, ganglions and nerve endings (form peripheral part of the nervous system
).
Functions of the human nervous system:
■ unites all parts of the body into a single whole ( integration );
■ regulates and coordinates the work of various organs and systems ( agreement );
■ carries out the connection of the organism with the external environment, its adaptation to environmental conditions and survival in these conditions ( reflection and adaptation );
■ provides (in interaction with the endocrine system) the constancy of the internal environment of the body at a relatively stable level ( correction );
■ determines the consciousness, thinking and speech of a person, his purposeful behavioral, mental and creative activity (activity ).
❖ Division of the nervous system according to functional characteristics:
■ somatic (innervates the skin and muscles; perceives the effects of the external environment and causes contractions of the skeletal muscles); obeys the will of man;
■ autonomous , or vegetative (regulates metabolic processes, growth and reproduction, the work of the heart and blood vessels, internal organs and endocrine glands).
Spinal cord
Spinal cord located in the spinal canal of the spine, starts from the medulla oblongata (above) and ends at the level of the second lumbar vertebra. It is a white cylindrical cord (cord) with a diameter of about 1 cm and a length of 42-45 cm. The spinal cord has two deep grooves in front and behind, dividing it into the right and left halves.
In the longitudinal direction of the spinal cord, one can distinguish 31 segment , each of which has two front and two back spine formed by axons of neurons; while all segments form a single whole.
Inside spinal cord is located Gray matter , which has (in cross section) the characteristic shape of a flying butterfly, the “wings” of which form front, rear and (in the thoracic region) lateral horns .
Gray matter consists of bodies of intercalary and motor neurons. Along the axis of gray matter along the spinal cord runs a narrow spinal drip , filled cerebrospinal fluid (see below).
On the periphery spinal cord (around gray matter) white matter .
white matter located in the form of 6 columns around the gray matter (two anterior, lateral and posterior).
It is made up of axons assembled in ascending (located in the back and side columns; transmit excitation to the brain) and descending (located in the anterior and lateral columns; transmit excitation from the brain to the working organs) pathways spinal cord.
The spinal cord is protected by rattling sheaths: solid (from the connective tissue that lines the spinal canal) gossamer (in the form of a thin network; contains nerves and vessels) and soft , or vascular (contains many vessels; grows together with the surface of the brain). The space between the arachnoid and soft shells is filled with cerebrospinal fluid, which provides optimal conditions for the vital activity of nerve cells and protects the spinal cord from shocks and concussions.
IN anterior horns segments of the spinal cord (they are located closer to the abdominal surface of the body) are the body motor neurons , from which their axons depart, forming the anterior motor roots , through which excitation is transmitted from the brain to the working organ (these are the longest human cells, their length can reach 1.3 m).
IN posterior horns segments are bodies intercalary neurons ; rear fit them sensitive roots , formed by the axons of sensory neurons that transmit excitation to the spinal cord. The cell bodies of these neurons are located in spinal nodes (ganglia) located outside the spinal cord along the sensory neurons.
In the thoracic region there are lateral horns Where are the bodies of neurons located? sympathetic parts autonomous nervous system.
Outside the spinal canal, the sensory and motor roots extending from the posterior and anterior horns of one "wing" of the segment unite, forming (together with the nerve fibers of the autonomic nervous system) a mixed spinal nerve , which contains both centripetal (sensory) and centrifugal (motor) fibers (see below).
❖ Spinal Cord Functions carried out under the control of the brain.
■ Reflex function:
pass through the gray matter of the spinal cord arcs unconditioned reflexes
(they do not affect human consciousness), regulating
visceral function, vascular lumen, urination, sexual function, diaphragmatic contraction, defecation, sweating, and managers
skeletal muscles; (examples, knee jerk:
lifting the leg when hitting the tendon attached to the kneecap; limb withdrawal reflex: under the action of a painful stimulus, reflex muscle contraction and limb withdrawal occur; urination reflex: filling the bladder causes excitation of stretch receptors in its wall, which leads to relaxation of the sphincter, contraction of the bladder walls and urination). 
When the spinal cord is ruptured above the arc of the unconditioned reflex, this reflex does not experience the regulatory action of the brain and is perverted (deviates from the norm, i.e. becomes pathological).
■ Conductor function; pathways of the white matter of the spinal cord are conductors of nerve impulses: ascending pathways nerve impulses from the gray matter of the spinal cord go into the brain (nerve impulses coming from sensitive neurons first enter the gray matter of certain segments of the spinal cord, where they undergo preliminary processing), and descending the paths they go from the brain to different segments of the spinal cord and from there along the spinal nerves to the organs.
In humans, the spinal cord controls only simple motor acts; complex movements (walking, writing, labor skills) are carried out with the obligatory participation of the brain.
Paralysis- loss of the ability to voluntary movements of the organs of the body, which occurs when the cervical spinal cord is damaged, resulting in a violation of the connection of the brain with the organs of the body located below the site of injury.
spinal shock- this is the disappearance of all reflexes and voluntary movements of the body's organs, the nerve centers of which lie below the site of injury, arising from injuries of the spine and disruption of communication between the brain and the underlying (in relation to the site of injury) sections of the spinal cord.
Nerves. Propagation of a nerve impulse
Nerves- these are strands of nervous tissue that connect the brain and nerve nodes with other organs and tissues of the body through nerve impulses transmitted through them.
Nerves are formed from several bundles nerve fibers (up to 106 fibers in total) and a small number of thin blood vessels enclosed in a common connective tissue sheath. For each nerve fiber, the nerve impulse propagates in isolation, without passing to other fibers.
■ Most nerves mixed ; they include fibers of both sensory and motor neurons.
nerve fiber- a long (may be more than 1 m long) thin process of a nerve cell ( axon), strongly branching at the very end; serves to transmit nerve impulses.
❖ Classification of nerve fibers depending on the structure: myelinated and unmyelinated .
Myelinated nerve fibers are covered with a myelin sheath. myelin sheath performs the functions of protecting, nourishing and isolating nerve fibers. It has a protein-lipid nature and is a plasmalemma Schwann cell (named after its discoverer T. Schwann, 1810-1882), which repeatedly (up to 100 times) wraps around the axon; while the cytoplasm, all organelles and the shell of the Schwann cell are concentrated on the periphery of the shell above the last turn of the plasmalemma. Between adjacent Schwann cells are open areas axon - interceptions of Ranvier . A nerve impulse along such a fiber propagates in jumps from one interception to another at a high speed - up to 120 m / s.
Unmyelinated nerve fibers are covered only by a thin insulating and myelin-free sheath. The speed of propagation of a nerve impulse along an unmyelinated nerve fiber is 0.2–2 m/s.
nerve impulse- This is a wave of excitation that propagates along the nerve fiber in response to irritation of the nerve cell.
■ The speed of propagation of a nerve impulse along the fiber is directly proportional to square root from the fiber diameter.
Mechanism of nerve impulse propagation. Simplified, a nerve fiber (axon) can be represented as a long cylindrical tube with a surface membrane separating two aqueous solutions of different chemical composition and concentration. The membrane has numerous valves that close when boosted electric field(i.e. with an increase in the difference of its potentials) and open when it is weakened. In the open state, some of these valves pass Na + ions, other valves pass K + ions, but all of them do not pass large ions. organic molecules.
Each axon is a microscopic powerhouse, dividing (through chemical reactions) electric charges. When the axon not excited , inside it there is an excess (compared to the environment surrounding the axon) of potassium cations (K +), as well as negative ions (anions) of a number of organic molecules. Outside the axon there are sodium cations (Na +) and chloride anions (C1 -), which are formed due to the dissociation of NaCl molecules. Anions of organic molecules are concentrated on internal membrane surface, charging it negative , and sodium cations - on its external surface, charging it positively . As a result, an electric field arises between the inner and outer surfaces of the membrane, the potential difference (0.05 V) of which ( resting potential) is large enough to keep the diaphragm valves closed. The resting potential was first described and measured in 1848-1851. German physiologist E.G. Dubois-Reymond in experiments on frog muscles.
When an axon is stimulated, the density of electric charges on its surface decreases, the electric field weakens, and the membrane valves open slightly, allowing the sodium cation Na + into the axon. These cations partially compensate for the negative electric charge the inner surface of the membrane, as a result of which, at the site of irritation, the direction of the field changes to the opposite. The process involves neighboring sections of the membrane, which gives rise to the spread of a nerve impulse. At this moment, the valves open, letting potassium cations K + out, due to which the negative charge inside the axon is gradually restored again, and the potential difference between the inner and outer surfaces of the membrane reaches a value of 0.05 V, characteristic of an unexcited axon. Thus, it is actually not an electric current that propagates along the axon, but a wave of an electrochemical reaction.
■ The shape and speed of propagation of the nerve impulse does not depend on the degree of irritation of the nerve fiber. If it is very strong, there is a whole series of identical impulses; if it is very weak, the impulse does not appear at all. Those. exists some minimum "threshold" degree of stimulation, below which the impulse is not excited.
Impulses entering the neuron along the nerve fiber from any receptor differ only in the number of signals in the series. This means that the neuron only needs to count the number of such signals in one series and, in accordance with the “rules”, how to respond to a given number of consecutive signals, send the necessary command to one or another organ.
spinal nerves
Every spinal nerve formed from two roots , extending from the spinal cord: front (efferent) root and rear (afferent) root, which are connected in the intervertebral foramen, forming mixed nerves (contain motor, sensory and sympathetic nerve fibers).
■ A person has 31 pairs of spinal nerves (according to the number of segments of the spinal cord) extending to the right and left of each segment.
Functions of the spinal nerves:
■ they cause sensitivity of the skin of the upper and lower extremities, chest, abdomen;
■ carry out the transmission of nerve impulses that ensure the movement of all parts of the body and limbs;
■ innervate skeletal muscles (diaphragm, intercostal muscles, muscles of the walls of the chest and abdominal cavities), causing their involuntary movements; at the same time, each segment innervates strictly defined areas of the skin and skeletal muscles.
Voluntary movements are carried out under the control of the cerebral cortex.
❖ Innervation by segments of the spinal cord:
■ segments of the cervical and upper thoracic parts of the spinal cord innervate the organs of the chest cavity, heart, lungs, muscles of the head and upper limbs;
■ the remaining segments of the thoracic and lumbar parts of the spinal cord innervate the organs of the upper and middle parts of the abdominal cavity and the muscles of the body;
■ The lower lumbar and sacral segments of the spinal cord innervate the organs of the lower part of the abdominal cavity and the muscles of the lower extremities.
cerebrospinal fluid
cerebrospinal fluid- a transparent, almost colorless liquid containing 89% water. Changes 5 times a day.
❖ Functions of cerebrospinal fluid:
■ creates a mechanical protective "cushion" for the brain;
■ is the internal environment from which the nerve cells of the brain receive nutrients;
■ participates in the removal of exchange products;
■ participates in the maintenance of intracranial pressure.
Brain. General characteristics of the structure
Brain located in the cranial cavity and covered with three meninges, equipped with vessels; its mass in an adult is 1100-1700 g.
❖Structure: the brain is made up of 5 departments:
■ medulla oblongata,
■ hindbrain,
■ midbrain,
■ diencephalon,
■ forebrain. 
brain stem - it is a system formed by the medulla oblongata, hindbrain pons, midbrain and diencephalon
In some textbooks and manuals, not only the pons of the hindbrain, but the entire hindbrain, including both the pons varolii and the cerebellum, are referred to the trunk of the brain bridge.
In the brainstem are the nuclei of the cranial nerves that connect the brain with the sense organs, muscles and some glands; gray the substance in it is inside in the form of nuclei, white - outside . White matter consists of processes of neurons that connect parts of the brain to each other.
Bark the cerebral hemispheres and the cerebellum is formed by gray matter, consisting of the bodies of neurons.
Inside the brain are communicating cavities ( cerebral ventricles ), which are a continuation of the central canal of the spinal cord and filled cerebrospinal fluid: I and II lateral ventricles - in the hemispheres of the forebrain, III - in the diencephalon, IV - in the medulla oblongata.
The channel connecting the IV and III ventricles and passing through the midbrain is called aqueduct of the brain.
12 pairs depart from the nuclei of the brain cranial nerves , innervating the sense organs, tissues of the head, neck, organs of the chest and abdominal cavities.
The brain (like the spinal cord) is covered with three shells: solid (from dense connective tissue; performs a protective function), gossamer (contains nerves and vessels) and vascular (contains many vessels). The space between the arachnoid and choroid is filled cerebral fluid .
The existence, location and function of the various centers of the brain are determined by stimulation various structures of the brain electric shock .
Medulla
Medulla is a direct continuation of the spinal cord (after it passes through the foramen magnum) and has a structure similar to it; at the top it borders on the bridge; it contains the fourth ventricle. White matter is located mainly on the outside and forms 2 protrusions - pyramids , the gray matter is located inside the white matter, forming in it numerous nuclei .
■ The nuclei of the medulla oblongata control many vital functions; that's why they are called centers .
❖ Functions of the medulla oblongata:
■ conductive: sensory and motor pathways pass through it, along which impulses are transmitted from the spinal cord to the overlying parts of the brain and back;
■ reflex(carried out together with the pons varolii): in centers the medulla oblongata closes the arcs of many important unconditioned reflexes: respiration and circulation , as well as sucking, salivation, swallowing, gastric secretion (responsible for digestive reflexes ), coughing, sneezing, vomiting, blinking (responsible for defensive reflexes ), etc. Damage to the medulla oblongata leads to cardiac and respiratory arrest and instant death.
Hind brain
Hind brain consists of two departments - pons and cerebellum .
Bridge (Varolian bridge) located between the medulla oblongata and midbrain; Nerve pathways pass through it, connecting the forebrain and midbrain with the medulla oblongata and spinal cord. The facial and auditory cranial nerves depart from the bridge.
❖ Functions of the hindbrain: together with the medulla oblongata, the bridge performs conductive And reflex functions as well governs digestion, respiration, cardiac activity, movement of the eyeballs, contraction of facial muscles that provide facial expressions, etc.
Cerebellum located above the medulla oblongata and consists of two small lateral hemispheres , the middle (most ancient, stem) part, connecting the hemispheres and called cerebellar worm , and three pairs of legs connecting the cerebellum with the midbrain, pons varolii and medulla oblongata.
The cerebellum is covered bark from the gray matter, under which is the white matter; the vermis and cerebellar peduncles also consist of white matter. Within the white matter of the cerebellum are nuclei made up of gray matter. The cerebellar cortex has numerous elevations (gyrus) and depressions (sulci). Most cortical neurons are inhibitory.
❖ Functions of the cerebellum:
■ the cerebellum receives information from the muscles, tendons, joints and motor centers of the brain;
■ it ensures the maintenance of muscle tone and body posture,
■ coordinates body movements (makes them accurate and coordinated);
■ manages balance.
With the destruction of the cerebellar vermis, a person cannot walk and stand, with damage to the hemispheres of the cerebellum, speech and writing are disturbed, severe trembling of the limbs appears, movements of the arms and legs become sharp.
Reticular Formation
Reticular (mesh) formation- This is a dense network formed by a cluster of neurons of different sizes and shapes, with well-developed processes that run in different directions and many synaptic contacts.
■ The reticular formation is located in the middle part of the medulla oblongata, in the pons and midbrain.
❖ Functions reticular formation:
■ its neurons sort (pass, delay or supply additional energy) incoming nerve impulses;
■ it regulates the excitability of all parts of the nervous system located above it ( ascending influences ) and below ( downward influences ), and is a center that stimulates the centers of the cerebral cortex;
■ the state of wakefulness and sleep is associated with its activity;
■ it ensures the formation of sustainable attention, emotions, thinking and consciousness;
■ with its participation, the regulation of digestion, respiration, heart activity, etc. is carried out.
midbrain
midbrain- the smallest part of the brain located above the bridge between the diencephalon and the cerebellum. Introduced quadrigemina (2 upper and 2 lower tubercles) and legs of the brain . There is a canal in its center water pipes ), connecting the III and IV ventricles and filled with cerebrospinal fluid.
❖ Midbrain functions:
■conductive: in its legs there are ascending nerve pathways to the cerebral cortex and cerebellum and descending nerve pathways along which impulses go from the cerebral hemispheres and cerebellum to the medulla oblongata and spinal cord;
■ reflex: associated with it are reflexes of body posture, its rectilinear motion, rotation, ascent, descent and landing, arising with the participation of the sensory system of balance and providing coordination of movement in space;
■ in the quadrigemina there are subcortical centers of visual and auditory reflexes that provide orientation towards sound and light. The neurons of the superior colliculus of the quadrigemina receive impulses from the eyes and muscles of the head and respond to objects moving rapidly in the field of view; neurons of the inferior colliculus respond to strong, sharp sounds, putting the auditory system on high alert;
■ it regulates muscle tone , provides small movements fingers, chewing.
diencephalon
❖ diencephalon- this is the final section of the brain stem; it is located under the cerebral hemispheres of the forebrain above the midbrain. It contains centers that process nerve impulses entering the cerebral hemispheres, as well as centers that control the activity of internal organs.
The structure of the diencephalon: it consists of the central part - thalamus (visual tubercles), hypothalamus (subtubercular region) and cranked bodies ; it also contains the third ventricle of the brain. Located at the base of the hypothalamus pituitary.
■ thalamus- this is a kind of "control room", through which all information about external environment and state of the body. The thalamus controls the rhythmic activity of the cerebral hemispheres, is the subcortical center for analysis of all types sensations , except for olfactory; it houses the centers that regulate sleep and wakefulness, emotional reactions(feelings of aggression, pleasure and fear) and mental activity person. IN ventral nuclei thalamus is formed sensation pain and maybe feeling time .
If the thalamus is damaged, the nature of sensations can change: for example, even slight touches on the skin, sound or light can cause severe attacks of pain in a person; on the contrary, sensitivity may decrease so much that a person will not respond to any irritation.
■ Hypothalamus- the highest center of vegetative regulation. He perceives changes in the internal environment body and regulates metabolism, body temperature, blood pressure, homeostasis, endocrine glands. It has centers hunger, satiety, thirst, regulation body temperature etc. It releases biologically active substances ( neurohormones ) and substances necessary for the synthesis of neurohormones pituitary gland , carrying out neurohumoral regulation the vital activity of the organism. The anterior nuclei of the hypothalamus are the center of parasympathetic autonomic regulation, the posterior nuclei are sympathetic.
■ Pituitary- lower appendage of the hypothalamus; is an endocrine gland (for details, see "").
Forebrain. The cerebral cortex
❖ forebrain represented by two large hemispheres And corpus callosum connecting the hemispheres. The large hemispheres control the work of all organ systems and provide the relationship of the body with the external environment. The corpus callosum plays an important role in the processing of information in the learning process.
big hemispheres two - solder and left ; they cover the midbrain and diencephalon. In an adult, the cerebral hemispheres account for up to 80% of the mass of the brain.
On the surface of each hemisphere there are many furrows (recesses) and convolutions (folds).
Main furrows; central, lateral and parietal-occipital. Furrows divide each hemisphere into 4 shares (see below); which, in turn, are divided by furrows into a series convolutions .
Inside the cerebral hemispheres are the 1st and 2nd ventricles of the brain.
The major hemispheres are covered gray matter - bark , consisting of several layers of neurons that differ from each other in shape, size and function. In total, there are 12-18 billion bodies of neurons in the cerebral cortex. The thickness of the bark is 1.5-4.5 mm, the area is 1.7-2.5 thousand cm2. Furrows and convolutions significantly increase the surface area and volume of the cortex (2/3 of the cortical area is hidden in the furrows).
The right and left hemispheres are functionally different from each other ( functional asymmetry of the hemispheres ). The presence of functional asymmetry of the hemispheres was established in experiments on people with a "split brain".
■ Operation " brain splitting a" consists in surgical cutting (according to medical indications) of all direct connections between the hemispheres, as a result of which they begin to function independently of each other.
At right-handers the leading (dominant) hemisphere is left , and at left-handed - right .
■ Right hemisphere responsible for creative thinking , forms the basis creativity , acceptance non-standard solutions . Damage to the visual zone of the right hemisphere leads to impaired face recognition.
■ Left hemisphere provides logical reasoning And abstract thinking (the ability to operate with mathematical formulas, etc.), it contains centers oral and written speeches , formation decisions . Damage to the visual zone of the left hemisphere leads to impaired recognition of letters and numbers.
Despite its functional asymmetry, the brain functions as whole , providing consciousness, memory, thinking, adequate behavior, various types of conscious human activity.
❖ Functions of the cortex cerebral hemispheres:
■ carries out higher nervous activity (consciousness, thinking, speech, memory, imagination, the ability to write, read, count);
■ provides the relationship of the body with the external environment, is the central department of all analyzers; various sensations are formed in its zones (the zones of hearing and taste are located in the temporal lobe; vision - in the occipital; speech - in the parietal and temporal; skin-muscle sense - in the parietal; movement - in the frontal);
■ provides mental activity;
■ arcs of conditioned reflexes are closed in it (ie, it is an organ for acquiring and accumulating life experience).
❖Lobes of the bark- subdivision of the surface of the cortex according to the anatomical principle: in each hemisphere, the frontal, temporal, parietal and occipital lobes are distinguished. 
❖ Cortex zone- a section of the cerebral cortex, characterized by the uniformity of the structure and functions performed.
❖ Types of cortical zones: sensory (or projection), associative, motor.
Sensory or projection zones are the higher centers various kinds sensitivity; when they are irritated, the simplest sensations arise, and when damaged, a violation of sensory functions occurs (blindness, deafness, etc.). These zones are located in the areas of the cortex, where the ascending pathways end, along which nerve impulses from the receptors of the sense organs (visual zone, auditory zone, etc.) are conducted.
■ visual area located in the occipital region of the cortex;
■olfactory, gustatory and auditory areas - in the temporal region and next to it;
■ skin and muscle sensation zones - in the posterior central gyrus.
Association zones- areas of the cortex responsible for generalized information processing; processes that ensure the mental functions of a person take place in them - thinking, speech, emotions, etc.
In associative zones, excitation occurs when impulses arrive not only in these, but also in sensory zones, and not only from one, but also simultaneously from several sense organs (for example, excitation in the visual zone can appear in response not only to visual, but also to auditory stimuli).
■ Frontal associative areas of the cortex provide the development of sensory information and form the goal and program of action, consisting of commands sent to the executive organs. From these organs, the frontal associative zones receive feedback about the implementation of actions and their direct consequences. In the frontal associative zones, this information is analyzed, it is determined whether the goal has been achieved, and if it is not achieved, the commands to the organs are corrected.
■ The development of the frontal lobes of the cortex largely determined high level mental abilities of humans compared to primates.
Motor (motor) zones- areas of the cortex, irritation of which causes muscle contraction. These zones control voluntary movements; they originate descending conducting paths along which nerve impulses go to the intercalary and executive neurons.
■ The motor function of various parts of the body is represented in the anterior central gyrus. The largest space is occupied by the motor zones of the hands, fingers and muscles of the face, the smallest - by the zones of the muscles of the body.
Electroencephalogram
Electroencephalogram (EEG)- this is a graphical record of the total electrical activity of the cerebral cortex - nerve impulses generated by a combination of its (cortex) neurons.
■ In the human EEG, waves of electrical activity of different frequencies are observed - from 0.5 to 30 oscillations per second.
Basic rhythms of electrical activity cerebral cortex: alpha rhythm, beta rhythm, delta rhythm and theta rhythm.
alpha rhythm- oscillations with a frequency of 8-13 hertz; this rhythm prevails over others during sleep.
beta rhythm has an oscillation frequency of more than 13 hertz; it is characteristic of active wakefulness.
Theta rhythm- oscillations with a frequency of 4-8 hertz.
delta rhythm has a frequency of 0.5-3.5 hertz.
■ Theta and delta rhythms are observed during very deep sleep or anesthesia .
cranial nerves
cranial nerves a person has 12 pairs; they depart from different parts of the brain and are divided by function into sensory, motor and mixed.
❖ Sensitive nerves-1, II, VIII couples:
■ I couple — olfactory nerves that depart from the forebrain and innervate the olfactory region of the nasal cavity;
■ And couple — visual nerves that depart from the diencephalon and innervate the retina of the eye;
■ VIII pair - auditory (or vestibulocochlear e) nerves; depart from the bridge, innervate the membranous labyrinth and the Cor-ti's organ of the inner ear.
❖ Motor nerves- III, IV, VI, X, XII pairs:
■ III pair — oculomotor nerves arising from the midbrain;
■ IV pair — blocky nerves also arise from the midbrain;
■ VI - diverting nerves that depart from the bridge (III, IV and VI pairs of nerves innervate the muscles of the eyeball and eyelids);
■ XI - additional nerves, depart from the medulla oblongata;
■XII— sublingual nerves also depart from the medulla oblongata (XI and XII pairs of nerves innervate the muscles of the pharynx, tongue, middle ear, parotid salivary gland).
❖ mixed nerves-V, VII, IX, X pairs:
■ V pair — trigeminal nerves that depart from the bridge, innervate the scalp, eye membranes, masticatory muscles, etc .;
■ VII pair - facial nerves also depart from the bridge, innervate the facial muscles, the lacrimal gland, etc .;
■ IX couple — glossopharyngeal nerves that depart from the diencephalon, innervate the muscles of the pharynx, middle ear, parotid salivary gland;
■ X pair — wandering nerves also depart from the diencephalon, innervate the muscles of the soft palate and larynx, the organs of the chest (trachea, bronchi, heart, slowing down its work) and abdominal cavities (stomach, liver, pancreas).
Features of the autonomic nervous system
Unlike the somatic nervous system, whose nerve fibers are thick, covered with a myelin sheath and are characterized by a high speed of propagation of nerve impulses, autonomic nerve fibers are usually thin, do not have a myelin sheath and are characterized by a low speed of propagation of nerve impulses (see table). 
❖ Functions of the autonomic nervous system:
■ maintaining the constancy of the internal environment of the body through the neuroregulation of tissue metabolism ("start", correction or suspension of certain metabolic processes) and the work of internal organs, the heart and blood vessels;
■ adaptation of the activities of these organs to the changed environmental conditions and the needs of the body.
The autonomic nervous system is made up of sympathetic And parasympathetic parts , which have the opposite effect on the physiological functions of organs.
sympathetic part autonomic nervous system creates conditions for intensive activity of the body, especially in extreme conditions when it is necessary to show all the possibilities of the organism.
parasympathetic part(the "retreat" system) of the autonomic nervous system reduces the level of activity, which contributes to the restoration of resources spent by the body.
■ Both parts (sections) of the autonomic nervous system are subordinate to higher nerve centers located in hypothalamus , and complement each other.
■ The hypothalamus coordinates the work of the autonomic nervous system with the activity of the endocrine and somatic systems.
■ Examples of the influence of the sympathetic and parasympathetic parts of the ANS on the organs are given in the table on p. 520.
The effective performance of the functions of both parts of the autonomic nervous system is ensured double innervation internal organs and heart.
double innervation internal organs and the heart means that nerve fibers from both the sympathetic and parasympathetic parts of the autonomic nervous system approach each of these organs. 
Neurons of the autonomic nervous system synthesize various mediators (acetylcholine, norepinephrine, serotonin, etc.) involved in the transmission of nerve impulses.
main feature autonomic nervous system - bineuronality of the efferent pathway
. This means that in the autonomic nervous system efferent
, or centrifugal
(i.e. coming from the head and spinal brain to organs
), nerve impulses sequentially pass through the bodies of two neurons. The two-neuronality of the efferent pathway makes it possible to distinguish in the sympathetic and parasympathetic parts of the autonomic nervous system central and peripheral parts
.
central part (nerve centers ) autonomic nervous system located in the central nervous system (in the lateral horns of the gray matter of the spinal cord, as well as in the medulla oblongata and midbrain) and contains the first motor neurons of the reflex arc . The autonomic nerve fibers going from these centers to the working organs switch in the autonomic ganglia of the peripheral part of the autonomic nervous system.
peripheral part The autonomic nervous system is located outside the central nervous system and consists of ganglion (nerve ganglions) formed by the bodies second motor neurons of the reflex arc as well as nerves and nerve plexuses.
■ At sympathetic department, these ganglia form a pair sympathetic chains (trunks) located near the spine on both sides of it, in the parasympathetic department they lie near or inside the innervated organs.
■ Postganglionic parasympathetic fibers approach the eye muscles, larynx, trachea, lungs, heart, lacrimal and salivary glands, muscles and glands of the digestive tract, excretory and genital organs. 
Causes of disruption of the nervous system
❖ Overwork of the nervous system weakens its regulatory function and can provoke the occurrence of a number of mental, cardiovascular, gastrointestinal, skin and other diseases.
❖ hereditary diseases can lead to changes in the activity of some enzymes. As a result, toxic substances accumulate in the body, the impact of which leads to impaired brain development and mental retardation.
Negative environmental factors:
■bacterial infections lead to the accumulation of toxins in the blood, poisoning the nervous tissue (meningitis, tetanus);
■ viral infections can affect the spinal cord (poliomyelitis) or the brain (encephalitis, rabies);
■ alcohol and its metabolic products excite various nerve cells (inhibitory or excitatory neurons), disorganizing the work of the nervous system; the systematic use of alcohol causes chronic depression of the nervous system, changes in skin sensitivity, muscle pain, weakening and even disappearance of many reflexes; irreversible changes occur in the central nervous system, forming personality changes and leading to the development of severe mental illness and dementia;
■ influence nicotine and drugs much like the effect of alcohol;
■heavy metal salts bind to enzymes, disrupting their work, which leads to disruption of the nervous system;
■ when bites of poisonous animals biologically active substances (poisons) that disrupt the functioning of neuronal membranes enter the bloodstream;
■ when head injuries, bleeding and severe pain possible loss of consciousness, which is preceded by: blackout, tinnitus, pallor, temperature drop, profuse sweat, weak pulse, shallow breathing.
Violation of cerebral circulation. The narrowing of the lumen of the brain vessels leads to disruption of the normal functioning of the brain and, as a result, to diseases of various organs. Injuries and high blood pressure can cause rupture of cerebral vessels, which usually leads to paralysis, disorders of the higher nervous activity or death.
Clamping of the nerve trunks of the brain causes severe pain. Infringement of the roots of the spinal cord by spasmodic back muscles or as a result of inflammation causes paroxysmal pain (typical for sciatica ), sensory disturbance ( numbness ) and etc.
❖ When metabolic disorders in the brain mental illness occurs
■neurosis - emotional, motor and behavioral disorders, accompanied by deviations from the autonomic nervous system and the work of internal organs (example: fear of the dark in children);
■ affective insanity - a more serious illness in which periods of extreme excitement alternate with apathy (paranoia, megalomania or persecution);
■ schizophrenia - splitting of consciousness;
■ hallucinations (may also occur with poisoning, high fever, acute alcoholic psychosis).
NERVOUS SYSTEM
a complex network of structures that permeates the entire body and ensures self-regulation of its vital activity due to the ability to respond to external and internal influences (stimuli). The main functions of the nervous system are the receipt, storage and processing of information from the external and internal environment, the regulation and coordination of the activities of all organs and organ systems. In humans, as in all mammals, the nervous system includes three main components: 1) nerve cells (neurons); 2) glial cells associated with them, in particular neuroglial cells, as well as cells that form neurilemma; 3) connective tissue. Neurons provide the conduction of nerve impulses; neuroglia performs supporting, protective and trophic functions both in the brain and spinal cord, and neurilemma, which consists mainly of specialized, so-called. Schwann cells, participates in the formation of sheaths of peripheral nerve fibers; connective tissue supports and links together the various parts of the nervous system. The human nervous system is divided in different ways. Anatomically, it consists of the central nervous system (CNS) and the peripheral nervous system (PNS). The central nervous system includes the brain and spinal cord, and the PNS, which provides communication between the central nervous system and various parts of the body, includes cranial and spinal nerves, as well as nerve nodes (ganglia) and nerve plexuses that lie outside the spinal cord and brain.
Neuron. The structural and functional unit of the nervous system is a nerve cell - a neuron. It is estimated that there are more than 100 billion neurons in the human nervous system. A typical neuron consists of a body (i.e., a nuclear part) and processes, one usually non-branching process, an axon, and several branching ones, dendrites. The axon carries impulses from the cell body to the muscles, glands, or other neurons, while the dendrites carry them to the cell body. In a neuron, as in other cells, there is a nucleus and a number of tiny structures - organelles (see also CELL). These include the endoplasmic reticulum, ribosomes, Nissl bodies (tigroid), mitochondria, the Golgi complex, lysosomes, filaments (neurofilaments and microtubules).
Nerve impulse. If the stimulation of a neuron exceeds a certain threshold value, then a series of chemical and electrical changes occur at the point of stimulation, which spread throughout the neuron. Transmitted electrical changes are called nerve impulses. Unlike a simple electrical discharge, which, due to the resistance of the neuron, will gradually weaken and be able to overcome only a short distance, a much slower "running" nerve impulse in the process of propagation is constantly restored (regenerates). The concentration of ions (electrically charged atoms) - mainly sodium and potassium, as well as organic matter- outside the neuron and inside it are not the same, so the nerve cell at rest is negatively charged from the inside, and positively from the outside; as a result, a potential difference arises on the cell membrane (the so-called "resting potential" is approximately -70 millivolts). Any change that reduces the negative charge inside the cell and thereby the potential difference across the membrane is called depolarization. The plasma membrane surrounding a neuron is a complex formation consisting of lipids (fats), proteins and carbohydrates. It is practically impermeable to ions. But some of the protein molecules in the membrane form channels through which certain ions can pass. However, these channels, called ionic channels, are not always open, but, like gates, they can open and close. When a neuron is stimulated, some of the sodium (Na +) channels open at the point of stimulation, due to which sodium ions enter the cell. The influx of these positively charged ions reduces the negative charge of the inner surface of the membrane in the region of the channel, which leads to depolarization, which is accompanied by a sharp change in voltage and a discharge - a so-called. "action potential", i.e. nerve impulse. The sodium channels then close. In many neurons, depolarization also causes potassium (K+) channels to open, causing potassium ions to flow out of the cell. The loss of these positively charged ions again increases the negative charge on the inner surface of the membrane. The potassium channels then close. Others are starting to work membrane proteins - so-called. potassium-sodium pumps that ensure the movement of Na + from the cell, and K + into the cell, which, along with the activity of potassium channels, restores the initial electrochemical state (resting potential) at the point of stimulation. Electrochemical changes at the point of stimulation cause depolarization at the adjacent point of the membrane, triggering the same cycle of changes in it. This process is constantly repeated, and at each new point where depolarization occurs, an impulse of the same magnitude is born as at the previous point. Thus, together with the renewed electrochemical cycle, the nerve impulse propagates along the neuron from point to point. Nerves, nerve fibers and ganglia. A nerve is a bundle of fibers, each of which functions independently of the others. The fibers in a nerve are organized into clusters surrounded by specialized connective tissue, which contains vessels that supply the nerve fibers with nutrients and oxygen and remove carbon dioxide and waste products. Nerve fibers along which impulses propagate from peripheral receptors to the central nervous system (afferent) are called sensitive or sensory. Fibers that transmit impulses from the central nervous system to muscles or glands (efferent) are called motor or motor. Most nerves are mixed and consist of both sensory and motor fibers. A ganglion (ganglion) is a cluster of neuron bodies in the peripheral nervous system. Axon fibers in the PNS are surrounded by a neurilemma - a sheath of Schwann cells that are located along the axon, like beads on a thread. A significant number of these axons are covered with an additional sheath of myelin (a protein-lipid complex); they are called myelinated (meaty). Fibers that are surrounded by neurilemma cells, but not covered with a myelin sheath, are called unmyelinated (non-myelinated). Myelinated fibers are found only in vertebrates. The myelin sheath is formed from the plasma membrane of the Schwann cells, which winds around the axon like a roll of ribbon, forming layer upon layer. The area of the axon where two adjacent Schwann cells touch each other is called the node of Ranvier. In the CNS, the myelin sheath of nerve fibers is formed by a special type of glial cells - oligodendroglia. Each of these cells forms the myelin sheath of several axons at once. Unmyelinated fibers in the CNS lack a sheath of any special cells. The myelin sheath accelerates the conduction of nerve impulses that "jump" from one node of Ranvier to another, using this sheath as a connecting electrical cable. The speed of impulse conduction increases with the thickening of the myelin sheath and ranges from 2 m / s (along unmyelinated fibers) to 120 m / s (along fibers, especially rich in myelin). For comparison: the propagation speed electric current on metal wires - from 300 to 3000 km / s.
Synapse. Each neuron has a specialized connection to muscles, glands, or other neurons. The zone of functional contact between two neurons is called a synapse. Interneuronal synapses are formed between different parts of two nerve cells: between an axon and a dendrite, between an axon and a cell body, between a dendrite and a dendrite, between an axon and an axon. A neuron that sends an impulse to a synapse is called presynaptic; the neuron receiving the impulse is postsynaptic. The synaptic space is slit-shaped. A nerve impulse propagating along the membrane of a presynaptic neuron reaches the synapse and stimulates the release of a special substance - a neurotransmitter - into a narrow synaptic cleft. Neurotransmitter molecules diffuse through the cleft and bind to receptors on the membrane of the postsynaptic neuron. If the neurotransmitter stimulates the postsynaptic neuron, its action is called excitatory; if it suppresses, it is called inhibitory. The result of the summation of hundreds and thousands of excitatory and inhibitory impulses simultaneously flowing to a neuron is the main factor determining whether this postsynaptic neuron will generate a nerve impulse in this moment. In a number of animals (for example, in the spiny lobster), a particularly close connection is established between the neurons of certain nerves with the formation of either an unusually narrow synapse, the so-called. gap junction, or, if neurons are in direct contact with each other, tight junction. Nerve impulses pass through these connections not with the participation of a neurotransmitter, but directly, by electrical transmission. A few dense junctions of neurons are also found in mammals, including humans.
Regeneration. By the time a person is born, all his neurons and most of the interneuronal connections have already been formed, and in the future only single new neurons are formed. When a neuron dies, it is not replaced by a new one. However, the remaining ones can take over the functions of the lost cell, forming new processes that form synapses with those neurons, muscles or glands with which the lost neuron was connected. Cut or damaged PNS neuron fibers surrounded by neurilemma can regenerate if the cell body remains intact. Below the site of transection, the neurilemma is preserved as a tubular structure, and that part of the axon that remains connected with the cell body grows along this tube until it reaches the nerve ending. Thus, the function of the damaged neuron is restored. Axons in the CNS that are not surrounded by a neurilemma are apparently unable to grow back to the site of their former termination. However, many CNS neurons can give rise to new short processes - branches of axons and dendrites that form new synapses.
CENTRAL NERVOUS SYSTEM
The CNS consists of the brain and spinal cord and their protective membranes. The outermost is the dura mater, under it is the arachnoid (arachnoid), and then the pia mater, fused with the surface of the brain. Between the soft and arachnoid membranes is the subarachnoid (subarachnoid) space containing the cerebrospinal (cerebrospinal) fluid, in which both the brain and the spinal cord literally float. The action of the buoyancy force of the fluid leads to the fact that, for example, the brain of an adult, having an average mass of 1500 g, actually weighs 50-100 g inside the skull. The meninges and cerebrospinal fluid also play the role of shock absorbers, softening all kinds of shocks and shocks that experiences the body and which could cause damage to the nervous system. The CNS is made up of gray and white matter. Gray matter is made up of cell bodies, dendrites, and unmyelinated axons, organized into complexes that include countless synapses and serve as information processing centers for many of the functions of the nervous system. White matter consists of myelinated and unmyelinated axons, which act as conductors that transmit impulses from one center to another. The composition of gray and white matter also includes glial cells. CNS neurons form many circuits that perform two main functions: they provide reflex activity, as well as complex information processing in higher brain centers. These higher centers, such as the visual cortex (visual cortex), receive incoming information, process it, and transmit a response signal along the axons. The result of the activity of the nervous system is one or another activity, which is based on the contraction or relaxation of muscles or the secretion or cessation of secretion of glands. It is with the work of muscles and glands that any way of our self-expression is connected. Incoming sensory information is processed by passing through a sequence of centers connected by long axons, which form specific pathways, such as pain, visual, auditory. Sensitive (ascending) pathways go in an ascending direction to the centers of the brain. Motor (descending) pathways connect the brain with the motor neurons of the cranial and spinal nerves. Pathways are usually organized in such a way that information (for example, pain or tactile) from the right side of the body goes to the left side of the brain and vice versa. This rule also applies to descending motor pathways: the right half of the brain controls the movements of the left half of the body, and the left half controls the right. From this general rule however, there are a few exceptions. The brain consists of three main structures: the cerebral hemispheres, the cerebellum, and the brainstem. The cerebral hemispheres - the largest part of the brain - contain higher nerve centers that form the basis of consciousness, intellect, personality, speech, and understanding. In each of the large hemispheres, the following formations are distinguished: isolated accumulations (nuclei) of gray matter lying in the depths, which contain many important centers; a large array of white matter located above them; covering the hemispheres from the outside, a thick layer of gray matter with numerous convolutions, constituting the cerebral cortex. The cerebellum also consists of a deep gray matter, an intermediate array of white matter, and an outer thick layer of gray matter that forms many convolutions. The cerebellum provides mainly coordination of movements. The brain stem is formed by a mass of gray and white matter, not divided into layers. The trunk is closely connected with the cerebral hemispheres, cerebellum and spinal cord and contains numerous centers of sensory and motor pathways. The first two pairs of cranial nerves depart from the cerebral hemispheres, the remaining ten pairs from the trunk. The trunk regulates such vital functions as breathing and blood circulation.
see also HUMAN BRAIN.
Spinal cord. Located inside the spinal column and protected by its bone tissue, the spinal cord has a cylindrical shape and is covered with three membranes. On a transverse section, the gray matter has the shape of the letter H or a butterfly. Gray matter is surrounded by white matter. The sensory fibers of the spinal nerves end in the dorsal (posterior) sections of the gray matter - the posterior horns (at the ends of H facing the back). The bodies of the motor neurons of the spinal nerves are located in the ventral (anterior) sections of the gray matter - the anterior horns (at the ends of H, remote from the back). In the white matter, there are ascending sensory pathways ending in the gray matter of the spinal cord, and descending motor pathways coming from the gray matter. In addition, many fibers in the white matter connect the different parts of the gray matter of the spinal cord.
PERIPHERAL NERVOUS SYSTEM
The PNS provides a two-way connection between the central parts of the nervous system and the organs and systems of the body. Anatomically, the PNS is represented by cranial (cranial) and spinal nerves, as well as a relatively autonomous enteric nervous system localized in the intestinal wall. All cranial nerves (12 pairs) are divided into motor, sensory or mixed. The motor nerves originate in the motor nuclei of the trunk, formed by the bodies of the motor neurons themselves, and the sensory nerves are formed from the fibers of those neurons whose bodies lie in the ganglia outside the brain. 31 pairs of spinal nerves depart from the spinal cord: 8 pairs of cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. They are designated according to the position of the vertebrae adjacent to the intervertebral foramen from which these nerves emerge. Each spinal nerve has an anterior and a posterior root that merges to form the nerve itself. The back root contains sensory fibers; it is closely related to the spinal ganglion (posterior root ganglion), which consists of the bodies of neurons whose axons form these fibers. The anterior root consists of motor fibers formed by neurons whose cell bodies lie in the spinal cord.
AUTONOMIC SYSTEM
The autonomic, or autonomic, nervous system regulates the activity of the involuntary muscles, the heart muscle, and various glands. Its structures are located both in the central nervous system and in the peripheral. The activity of the autonomic nervous system is aimed at maintaining homeostasis, i.e. a relatively stable state of the internal environment of the body, such as a constant body temperature or blood pressure corresponding to the needs of the body. Signals from the CNS arrive at the working (effector) organs through pairs of series-connected neurons. The bodies of neurons of the first level are located in the CNS, and their axons terminate in the autonomic ganglia lying outside the CNS, and here they form synapses with the bodies of neurons of the second level, the axons of which directly contact the effector organs. The first neurons are called preganglionic, the second - postganglionic. In that part of the autonomic nervous system, which is called the sympathetic, the bodies of preganglionic neurons are located in the gray matter of the thoracic (thoracic) and lumbar (lumbar) spinal cord. Therefore, the sympathetic system is also called the thoraco-lumbar system. The axons of its preganglionic neurons terminate and form synapses with postganglionic neurons in the ganglia located in a chain along the spine. Axons of postganglionic neurons are in contact with effector organs. The endings of postganglionic fibers secrete norepinephrine (a substance close to adrenaline) as a neurotransmitter, and therefore the sympathetic system is also defined as adrenergic. The sympathetic system is complemented by the parasympathetic nervous system. The bodies of its pregangliar neurons are located in the brainstem (intracranial, i.e. inside the skull) and the sacral (sacral) section of the spinal cord. Therefore, the parasympathetic system is also called the craniosacral system. Axons of preganglionic parasympathetic neurons terminate and form synapses with postganglionic neurons in the ganglia located near the working organs. The endings of postganglionic parasympathetic fibers release the neurotransmitter acetylcholine, on the basis of which the parasympathetic system is also called the cholinergic system. As a rule, the sympathetic system stimulates those processes that are aimed at mobilizing the body's forces in extreme situations or under stress. The parasympathetic system contributes to the accumulation or restoration of the body's energy resources. The reactions of the sympathetic system are accompanied by the consumption of energy resources, an increase in the frequency and strength of heart contractions, an increase in blood pressure and blood sugar, as well as an increase in blood flow to skeletal muscles due to a decrease in its flow to internal organs and skin. All of these changes are characteristic of the "fright, flight or fight" response. The parasympathetic system, on the contrary, reduces the frequency and strength of heart contractions, lowers blood pressure, and stimulates the digestive system. The sympathetic and parasympathetic systems act in a coordinated manner and cannot be regarded as antagonistic. Together they support the functioning of internal organs and tissues at a level corresponding to the intensity of stress and the emotional state of a person. Both systems function continuously, but their activity levels fluctuate depending on the situation.
REFLEXES
When an adequate stimulus acts on the receptor of a sensory neuron, a volley of impulses arises in it, triggering a response action, called a reflex act (reflex). Reflexes underlie most of the manifestations of the vital activity of our body. The reflex act is carried out by the so-called. reflex arc; this term refers to the path of transmission of nerve impulses from the point of initial stimulation on the body to the organ that performs the response. The arc of the reflex that causes contraction of the skeletal muscle consists of at least two neurons: a sensory neuron, whose body is located in the ganglion, and the axon forms a synapse with the neurons of the spinal cord or brain stem, and the motor (lower, or peripheral, motor neuron), whose body is located in gray matter, and the axon terminates in a motor end plate on skeletal muscle fibers. The reflex arc between the sensory and motor neurons can also include a third, intermediate, neuron located in the gray matter. The arcs of many reflexes contain two or more intermediate neurons. Reflex actions are carried out involuntarily, many of them are not realized. The knee jerk, for example, is elicited by tapping the quadriceps tendon at the knee. This is a two-neuron reflex, its reflex arc consists of muscle spindles (muscle receptors), a sensory neuron, a peripheral motor neuron, and a muscle. Another example is the reflex withdrawal of a hand from a hot object: the arc of this reflex includes a sensory neuron, one or more intermediate neurons in the gray matter of the spinal cord, a peripheral motor neuron, and a muscle. Many reflex acts have a much more complex mechanism. The so-called intersegmental reflexes are made up of combinations of simpler reflexes, in the implementation of which many segments of the spinal cord take part. Thanks to such reflexes, for example, coordination of the movements of the arms and legs when walking is ensured. The complex reflexes that close in the brain include movements associated with maintaining balance. Visceral reflexes, i.e. reflex reactions of internal organs mediated by the autonomic nervous system; they provide emptying of the bladder and many processes in the digestive system.
see also REFLEX.
DISEASES OF THE NERVOUS SYSTEM
Damage to the nervous system occurs with organic diseases or injuries of the brain and spinal cord, meninges, peripheral nerves. Diagnosis and treatment of diseases and injuries of the nervous system is the subject of a special branch of medicine - neurology. Psychiatry and clinical psychology deal mainly with mental disorders. The areas of these medical disciplines often overlap. See individual diseases of the nervous system: ALZHEIMER'S DISEASE;
STROKE ;
MENINGITIS;
NEURITIS;
PARALYSIS;
PARKINSON'S DISEASE;
POLIO;
MULTIPLE SCLEROSIS ;
TENETIS;
CEREBRAL PALSY ;
CHOREA;
ENCEPHALITIS;
EPILEPSY.
see also
ANATOMY COMPARATIVE;
HUMAN ANATOMY .
LITERATURE
Bloom F., Leizerson A., Hofstadter L. Brain, mind and behavior. M., 1988 Human Physiology, ed. R. Schmidt, G. Tevsa, vol. 1. M., 1996
Collier Encyclopedia. - Open society. 2000 .
